1. Field of the Invention
This invention relates to an apparatus, or system, for applying a multi-component liquid liner composition to the inner surface of a conduit, and in particular, well bore tubing, while the conduit remains in place. The invention also relates to methods for applying a multi-component liquid liner composition to the inner surface of conduits.
2. Description of Related Art
During the past several years, the oil and gas industry has been challenged to find new ways for improving operating efficiencies while meeting the ever increasing demand for oil and gas. With overall production output dropping below consumption levels, it has become increasingly important for producers to maximize their current production. This requires that they minimize any downtime when a well must be pulled out of service for workover operations.
One of the most costly workover operations is the pulling and replacement of the production tubulars, i.e., well bore tubing (“tubing”) or casing. These conduits are a primary means for pressure containment and oil and gas transfer during production. If the production tubulars fail, a loss of well control may result with the further possibility of an uncontrolled release of gas and oil from the well.
Many of the wells that are currently producing have developed wall thickness reductions in the well bore tubing that may eventually lead to a leak or failure. Wall thickness reductions usually occur due to corrosion and erosion over a period of time. Corrosion occurs when fluids, such as salt water or other corrosive fluids, are produced during normal oil and gas production. Certain fluids and gases chemically attack the metal of the well bore tubing causing general loss of wall thickness and localized pitting of the well bore tubing until the wall is eventually breached. Erosion causes wall thickness losses due to the physical contact and the gouging action of abrasive particles, such as sand, carried by the produced fluids.
One way to prevent corrosion and reduce erosion is to install tubing that has an internal protective coating. These coatings can reduce wall loss, greatly extending the life of the tubing and reducing the need for workover operations. However, internally coated tubing is very expensive and requires that the existing tubing be pulled and new tubing installed.
In another approach, a continuous length of solid lining material, e.g., plastic or polyethylene pipe, is inserted into the tubing of the well. The solid lining material is pulled into the conduit or inserted through an outside-diameter-reduction unit and held in tension with weight or other means until the solid lining material is sufficiently deformed to permit installation of the solid lining material into the conduit. The solid lining material is then positioned at, e.g., lowered to, the desired location in the conduit, e.g., at a zone located at a specific depth, e.g., 1,000 feet. The tension is then released and the solid lining material is allowed to relax and expand, or lay loosely, against the inner surface of the conduit.
This lining method has many disadvantages. For example, it requires expensive equipment that is not always available. Additionally, in some instances, sections of the plastic liner must be removed from inside of the conduit to allow valves and other assemblies in the conduit to function correctly. Moreover, this method is time consuming and problematic to perform due to varying dimensions and configurations of the valves and other assemblies in the production tubing. As such, this method generally requires special tools to be designed, fabricated, and operated for removing the plastic liner from the inside of each of these assemblies. This process also requires the use and transportation of large, specialized equipment for each operation. As mentioned above, the equipment is not readily available in many areas and it is contemplated that the equipment, when available, may not permit safe operations on pressure-containing conduits.
Another approach involves a method that requires placement or injection of a liquid coating between two pigs, or wiper plugs, and moving the wiper plugs at a pre-determined rate along the inner surface of the conduit over a desired distance. Liquid coating is located between the wiper plugs and is applied to the inner surface of the conduit between the wiper plugs as the wiper plugs move along the inner surface. This process is referred to as an “in-situ” coating because it permits the conduit to remain in place, or in its operational location, while the coating is applied.
While in-situ coating is used in various pipeline applications, it has not been successfully used in production tubular applications or many other applications due to various shortcomings. For example, in-situ coating methods require the use of a liquid coating material that will stay in a liquid state for extended periods of time to avoid curing, or hardening, between the wiper plugs while the plugs move along the inner surface of the conduit. Additionally, the use of wiper plugs requires two openings in the conduit. The first opening is the insertion point and the second opening is the exit point. Therefore, the wiper plugs move along the inner surface from the insertion point to the exit point.
Generally, the liquid coating material in this method is either a single component liquid, or a multi-component liquid that is mixed prior to transmitting the liquid to the application site, i.e., the location along the inner surface of the conduit desired to be coated by the liquid coating material. In these prior attempts, the liquid cures prematurely and prevents the successful coating of the inner surface of the tubing. For example, extended time periods for transmission of the liquid coating material through the conduit and elevated temperatures at the application site have been determined to cause these liquid coating materials to cure prematurely.
Additionally, because the conditions, e.g., temperature, pressure, humidity, etc., may vary at different application sites along the inner surface of the conduit, the premixed liquid cannot be customized for the varying conditions at the application sites. This lack of flexibility has resulted in liquid coating compositions that either cure too quickly, or, in many cases, not at all. Additionally, this practice does not allow the chemical(s) or liquid component(s) to be tailored during the process and may not be used when the conduit is limited to a single opening. Therefore, in many instances, the inner surface of the tubing is not adequately coated by the single or multi-component liquid coating compositions currently employed.
Accordingly, prior to the development of the present invention, there has been no system for applying a multi-component liquid liner composition to the inner surface of a conduit and method of applying a multi-component liquid liner composition to the inner surface of a conduit, which: permits in-situ coating of production tubulars without having the liquid coating composition cure prematurely; permits coating of the inner surface of the production tubulars without having to extract old tubing and replace with new tubing; permits the application site to be more easily targeted around valves and other assemblies; decreases the amount of time production of oil and gas is interrupted; permits independent, or isolated, transmission of liquid liner components to the application site; and is less expensive than tubing replacement using new conventional tubing or tubing that is pre-coated prior to installation in the well. Therefore, the art has sought a system for applying a multi-component liquid liner composition to the inner surface of a conduit and method of applying a multi-component liquid liner composition to the inner surface of a conduit which: permits in-situ coating of production tubulars without having the liquid coating composition cure prematurely; permits coating of the inner surface of the production tubulars without having to extract old tubing and replace with new tubing; permits the application site to be more easily targeted around valves and other assemblies; decreases the amount of time production of oil and gas is interrupted; permits independent, or isolated, transmission of liquid liner components to the application site; and is less expensive than tubing replacement using new tubing or tubing that is pre-coated prior to installation in the well.